Method of driving vibration actuator, drive device, and image pickup apparatus

Abstract

A drive device for a vibration actuator, which makes it possible to perform low-speed and stable driving and expand a dynamic range of driving speed, includes first and second switching circuits, a position detection sensor, and a microprocessing unit (MPU). The first switching circuit and the second switching circuit apply a first drive signal and a second drive signal, for exciting vibration, to an electromechanical energy conversion element of a vibrating body. The position detection sensor acquires information on a relative position between the vibrating body and a driven body in press contact with each other. The MPU switches the first and second drive signals to third drive and fourth drive signals, respectively, based on the acquired information, to thereby change a position at which a highest one of peaks of amplitude of vibration excited in the vibrating body is formed.

The invention claimed is: 
     
       1. A drive device for a vibration actuator that includes a vibrating body and a driven body in contact with each other, comprising:
 a drive unit configured to apply a first drive signal and a second drive signal to an electromechanical energy conversion element of the vibrating body; 
 an acquisition unit configured to acquire information on a relative position between the vibrating body and the driven body; and 
 a control unit configured to switch the first drive signal and the second drive signal to a third drive signal and a fourth drive signal, respectively, based on the relative position by switching a phase difference between the first drive signal and the second drive signal such that an envelope of a bundle of vibration waves generated based on the third drive signal and the fourth drive signal follows variation of the relative position between the vibrating body and the driven body. 
 
     
     
       2. The drive device according to  claim 1 , wherein switching of the first drive signal and the second drive signal to the third drive signal and the fourth drive signal is performed by fixing one of the first drive signal and the second drive signal, and changing the other drive signal. 
     
     
       3. The drive device according to  claim 1 , wherein the acquisition unit sets a predetermined number of pulses for a predetermined amount of movement of the driven body with respect to the vibrating body, and acquires the relative position between the vibrating body and the driven body as a value of the number of pulses. 
     
     
       4. The drive device according to  claim 1 , wherein both the vibrating body and the driven body have an annular shape and are arranged coaxially with each other,
 wherein the first drive signal and the second drive signal are applied to the electromechanical energy conversion element with a predetermined phase difference, whereby progressive vibration is excited in the vibrating body, 
 wherein the driven body has convex portions protruding toward the vibrating body on a sliding surface that slides on the vibrating body, and 
 wherein the control unit switches the first drive signal and the second drive signal to the third drive signal and the fourth drive signal, respectively, according to the relative movement between the vibrating body and the driven body, such that the convex portions of the driven body are brought into contact with the vibrating body at positions in a circumferential direction of the vibrating body at which the highest one of peaks of the amplitude of the progressive vibration generated in the vibrating body is formed, to thereby switch the position in the circumferential direction of the vibrating body at which the highest one of the peaks of the amplitude of the progressive vibration is formed. 
 
     
     
       5. The drive device according to  claim 1 , wherein the control unit stores a position at which a speed of the driven body with respect to the vibrating body becomes minimum or maximum when the electromechanical energy conversion element is driven in a state in which frequency of the first and second drive signals is not changed, and determines, with reference to the stored position, a position at which a highest one of peaks of amplitude of the progressive vibration generated in the vibrating body is formed. 
     
     
       6. The drive device according to  claim 1 , wherein the vibrating body includes a vibration detection unit configured to detect vibration generated in the vibrating body,
 wherein the control unit stores a position at which a phase difference between a signal from the vibration detection unit and the first drive signal or the second drive signal becomes minimum or maximum when the electromechanical energy conversion element is driven in a state in which frequency of the first and second drive signals is not changed, and determines, with reference to the stored position, a position at which a highest one of peaks of amplitude of the progressive vibration generated in the vibrating body is formed. 
 
     
     
       7. An image pickup apparatus comprising:
 a lens; 
 a vibration actuator that moves the lens in an optical axis direction; 
 an image pickup element that picks up an optical image formed by the lens; and 
 a drive device according to  claim 1 . 
 
     
     
       8. A vibration type driving apparatus comprising:
 a vibrating body; 
 a driven body in contact with the vibrating body; and 
 the drive device according to  claim 1 . 
 
     
     
       9. The drive device according to  claim 1 , wherein convex portions of the envelope of the bundle of vibration waves generated based on the third drive signal and the fourth drive signal follow convex portions of the driven body, which moves relatively to the vibrating body. 
     
     
       10. The drive device according to  claim 4 , wherein the number of times of operation for switching the position in the circumferential direction of the vibrating body at which the highest one of the peaks of the amplitude of the progressive vibration is formed is at least t×m×2, assuming that the number of the convex portions of the driven body is represented by t, and the number of waves of vibration formed per circumference of the vibrating body, which is calculated from an electrode pattern of the electromechanical energy conversion element, is represented by m. 
     
     
       11. A method of controlling a drive device for driving a vibration actuator that includes a vibrating body and a driven body in contact with each other, the method comprising:
 applying a first drive signal and a second drive signal to an electromechanical energy conversion element of the vibrating body; 
 acquiring information on a relative position between the vibrating body and the driven body; and 
 switching the first drive signal and the second drive signal to a third drive signal and a fourth drive signal, respectively, based on the relative position by switching a phase difference between the first drive signal and the second drive signal such that an envelope of a bundle of vibration waves generated based on the third drive signal and the fourth drive signal follows variation of the relative position between the vibrating body and the driven body. 
 
     
     
       12. The method of controlling the drive device according to  claim 11 , wherein convex portions of the envelope of the bundle of vibration waves generated based on the third drive signal and the fourth drive signal follow convex portions of the driven body, which moves relatively to the vibrating body. 
     
     
       13. A method of driving a vibration actuator including a vibrating body and a driven body in contact with the each other, the method comprising:
 applying a first drive signal and a second drive signal having a predetermined frequency to an electromechanical energy conversion element of the vibrating body with a fixed phase difference; 
 acquiring a speed profile indicative of a relationship between a position and a speed of the driven body with respect to the vibrating body; 
 detecting a lowest-speed position at which the speed of the driven body becomes lowest, from the acquired speed profile; and 
 acquiring information on a relative position between the driven body and the vibrating body, and switching the first drive signal and the second drive signal to a third drive signal and a fourth drive signal, respectively, based on the relative position and the lowest-speed position, by switching a phase difference between the first drive signal and the second drive signal such that an envelope of a bundle of vibration waves generated based on the third drive signal and the fourth drive signal follows variation of the relative position between the vibrating body and the driven body. 
 
     
     
       14. The method of driving the vibration actuator according to  claim 13 , wherein convex portions of the envelope of the bundle of vibration waves generated based on the third drive signal and the fourth drive signal follow convex portions of the driven body, which moves relatively to the vibrating body. 
     
     
       15. A method of driving a vibration actuator including a vibrating body and a driven body in contact with each other, the method comprising:
 applying a first drive signal and a second drive signal having a predetermined frequency to an electromechanical energy conversion element of the vibrating body with a fixed phase difference; 
 detecting vibration generated in the vibrating body; 
 acquiring a phase difference profile indicative of a relationship between a position of the driven body with respect to the vibrating body, and a phase difference between a signal produced by detecting the vibration and the first drive signal or the second drive signal; 
 detecting a lowest-phase difference position at which the phase difference becomes lowest, from the acquired phase difference profile; and 
 acquiring information on a relative position between the driven body and the vibrating body, and switching the first drive signal and the second drive signal to a third drive signal and a fourth drive signal, respectively, based on the relative position and the lowest-phase difference position, by switching a phase difference between the first drive signal and the second drive signal such that an envelope of a bundle of vibration waves generated based on the third drive signal and the fourth drive signal follows variation of the relative position between the vibrating body and the driven body. 
 
     
     
       16. The method of driving the vibration actuator according to  claim 15 , wherein convex portions of the envelope of the bundle of vibration waves generated based on the third drive signal and the fourth drive signal follow convex portions of the driven body, which moves relatively to the vibrating body.